1. Field of the Invention
The present invention relates to an equalizing filter, a control method for signal equalization, and a method of forming an inductor. Particularly, the present invention relates to an equalizing filter for equalizing an electrical reception signal to reshape its waveform, a control method for obtaining a signal equalized in the frequency domain so that it will exhibit better eye patterns, and a method of forming an inductor on a substrate.
2. Description of the Related Art
In the recent trend toward the "Information Age" society, there is a strong demand for highly efficient data communications networks capable of handling a variety of data in a large volume. The broadband ISDN (B-ISDN) have been studied and introduced aggressively as a core technology for such network infrastructures. Another important aspect of data communication is the cost of services. Economical and reliable optical networks are indispensable for low-cost communication services. As such, the optical communication technology plays a key role in realizing B-ISDN infrastructures, and to this end, the design of optical receivers is of particular importance in its actual implementation since a higher sensitivity promises a longer transmission distance.
FIG. 21 is a block diagram of a typical optical receiver 200 available today. This optical receiver 200 comprises: a photodetector PD to transduce the entered optical beam into an electrical signal, a preamplifier 201 to amplify the electrical signal, an equalizing filter 202 to shape the signal waveform by equalizing the frequency components contained therein, and a discrimination circuit 203 to detect the symbols for binary 1s and 0s.
In operation of the optical receiver 200, a given optical input signal is first converted into an electrical signal by the photodetector PD. Besides containing some undesired noise, this electrical signal is distorted due to the non-ideal characteristics of fiber optic transmission media. After being amplified by the preamplifier 201, the electrical signal with such distortion and noise is subjected to the equalizing filter 202, which is carefully designed to yield maximum signal-to-noise (S/N) ratios. The equalizing filter 202 reshapes the signal waveform and filters out the noise with its limited passband. After that, the discrimination circuit 203 determines the signal levels and produces logical is and 0s as its data outputs.
To maximize the sensitivity of the optical receiver 200 configured as above, it is necessary to optimize the frequency response so that the receiver will exhibit a wider aperture in so-called "eye pattern" tests. The eye pattern is a method for evaluating a data transmission system by using an oscilloscope to display received data bits in synchronization with the original transmission clock signal being used. The ideal rectangular edge between the "1" and "0" states appears rounded due to unwanted jitters and phase distortion, thus forming an eye-shaped pattern. Here, wider eye opening generally indicates better signal quality. To obtain a wider eye aperture in such tests, the above-described equalizing filter must have an adequate peaking characteristic in its frequency response, as well as an appropriate order of its roll-off characteristics.
Conventional equalizing filters, however, cannot provide stable operations at transmission rates as high as several gigabits per second. This is because the conventional filters contain some active components, such as transistors, which have little performance margins in that high frequency range. In addition, the frequency response of conventional equalizing filters can easily be affected by the variations in active components' device parameters, temperature changes, and fluctuations in supply voltages. Such factors cause adverse effect on the reliability and quality of those optical receiver products.